Prior art communication systems have endeavored to efficiently communicate information to receivers while extending battery life of the receivers at the expense of system throughput or vice versa. One prior art protocol provides a preamble signal which initially synchronizes the receivers to a protocol signal. One of the several well known preamble signals may be used, each identifying a different group of receivers which are used to decode message information.
The operation of the prior art communication system requires receivers to synchronously decode the received signal subsequent to being synchronized to the protocol signal. A receiver synchronized to the signal needs to search for its address in only a predetermined one of M frames. In the remaining M-1 frames, the receiver conserves power by one of the well known techniques of battery saving. However, when M is too small, the receivers have to sample the channel frequently which results in poor (or low) battery life and when is too large, the receivers sample the channel less frequently resulting in improved battery life but reduced message throughput.
It is desirable to provide battery saving features for the receiver during the absence of a signal being directed to the receiver. This has typically been accomplished with a preamble signal preceding the message transmission. The transmissions begin with a long preamble signal providing for receiver synchronization before the message transmission and providing for battery saving in the absence thereof. The preamble signal although providing for battery saving and synchronization, decreases the overall system message throughput. During the time taken for a preamble transmission, no message information can be communicated to the receivers, thereby decreasing throughput of the system.
Synchronous protocols eliminate preamble signal, thereby enabling a more efficient battery savings. A synchronous signal divides the receivers into one of a plurality of group fields, each group field occurring at a predetermined period and having a predetermined maximum message information capacity. Since the synchronous signal is always being transmitted, no preamble signals are required, and a receiver needs only decode information while its preassigned group is being transmitted. However, varying traffic demands (the amount of message information for a group of receivers) may cause the amount of message information for one group of receivers to exceed the maximum capacity of the group field while another group field has available capacity. This causes transmission of idle signals during one group field, while in another group field, numerous messages are being queued because its capacity is exceeded. The throughput of the overall system is decreased because selective overload patterns are generated from the varying traffic levels within different group fields.
Thus, what is needed is method and apparatus for efficiently transmitting information to receivers while extending battery life of the receivers and increasing the throughput of the communication system.